Computer storage systems can use multiple disks for storing information. For example, on storage area networks (SANs) a computer on the network can access various storage disks on the network. Similarly, RAID systems can provide multiple disks that can be accessed by a computer system. Multiple disks can be grouped into storage pools. Logical volumes are created that can be allocated space on one or more storage disks in one or more storage pools. Storage volumes may be created, expanded, deleted by a computer system. These activities consume or release storage from the storage pools. Each storage pool may include a number of different disk drives having different sizes. Since logical volumes may be created or expanded during the operation of a computer system, it is necessary to ensure that sufficient storage space exists in the storage pools to prevent the overwriting and loss of data, or the inability to create of expand volumes.